Because the "Fatal Error" specs specifically inject fatal errors during
execution, and do so by reacting to a "poison" event, the fatal error prevents
the poison event from being ACK'd in the underlying queue.
By specifying a one-off temporary data directory in these specs and cleaning up
after ourselves, we ensure that a PQ containing un-ACK'd events isn't leaked to
the next spec to run.
Currently, LS does not respect fatal errors such as java.lang.OutOfMemoryError and continues executing.
This is dangerous since JVM errors are a legitimate reason to halt the process and not continue processing.
Additionally:
- make sure we log the full stack-trace on fatal errors
- halt the JVM wout executing finalizers/hook (scissors on how ES handles uncaught exceptions)
- also, we should now be aware of a potentially unexpectedly dying thread
